How To Look At A House
McGarry and Madsen's home inspection blog for buyers of
site-built, mobile/manfuactured and modular homes
What is causing soft spots in my mobile/manufactured home floor?
Thursday, November 4, 2021
Soft spots in a mobile home floor are always caused by an area of long-term or repeated wetness, and it can come from above, below, or the side:
ABOVE - A poorly installed marriage line connection at the ridge line of a double-wide can allow a gap to open up and water to run down, sometimes along the roof framing, before it drops elsewhere to the floor. Ordinary roof leaks can also do it. Splashed water around a shower or tub, if done repeatedly and allowed to sit, is another culprit. Or the spilled water around pet food bowls.
BELOW - Leaking plumbing will drip into puddles on the belly board, creating a bulge, wet areas, and high humidity below the floor. Also, an oversize air conditioner can cause condensation on the wood subfloor. When the a/c unit is rated for significantly more BTUs than what is recommended by the manufacturer, the system will cool the home too quickly, not allowing the necessary air flow time over the evaporator coils to provide adequate dehumidification. Combine that with a thermostat set in the lower 70s, and condensation will wet the surface of the floor where the cold above and warm air below meet. Even worse, close a floor supply register, which pressurizes the connection of the duct to the register above, and see what the leaked cold air gushing into the enclosed floor structure voids will do.
A mobile home we inspected last month had a 5-ton package air conditioner connected to a double-wide rated by the manufacturer for a max 2.5 ton unit. Plus, the home was sited on continuously moist soil at the edge of a Florida swamp, and had large tears in the belly board. Then, to top it off, the homeowner had replaced his water heater at the inside laundry room with one of those new heat-pump units. It exhausts additional cold air into the home as part of heating the water. Condensation soft spots in the floor were everywhere, some with temporary patches nailed over them. Most of the floor, walls and ceiling in the area around the new water heater had been torn out, with mold showing on parts of the drywall that remained.
THE SIDE - Mobile homes are notorious for leaking rainwater at the bottom corner of windows. It runs down to the floor level and then spreads sideways, leaving a stain on the baseboard over time, and creating soft spots near the wall.
Particle board used in older manufactured homes is more susceptible to weakening from wetness than products like plywood and OSB, but all of them are eventually damaged by high moisture. The solution, of course, is to cut out and replace the bad areas after fixing the cause of the problem. But avoid making small repairs. The repair piece should go across at least two floor joist bays.
To learn more about other ways mosture can attack a mobile home, and there are plenty more, download HUD’s guide “Moisture Problems in Manufactured Homes, Understanding Their Causes and Finding Solutions”. Also see What causes a crowned floor in a mobile/manufactured home? and What are the signs that a mobile home is not level?
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